import { DEFAULT_SQL_FORMATTER_SETTINGS, type SqlFormatterSettings } from "@/lib/sqlFormatterConfig";

export const MAX_MONGO_FORMAT_CHARS = 1_000_000;

interface FormatState {
    out: string;
    indentLevel: number;
    atLineStart: boolean;
    pendingSpace: boolean;
    chainIndent: boolean;
    pendingChainCall: boolean;
    stack: Array<{ char: string; expanded: boolean; chainCall?: boolean }>;
}

const CHAIN_METHODS = new Set(["find", "findOne", "aggregate", "countDocuments", "distinct", "insertOne", "insertMany", "updateOne", "updateMany", "deleteOne", "deleteMany", "getIndexes", "createIndex", "sort", "limit", "skip"]);

export function formatMongoShellText(text: string, settings: Partial<SqlFormatterSettings> = DEFAULT_SQL_FORMATTER_SETTINGS): string {
    if (!text.trim()) return text;
    if (text.length > MAX_MONGO_FORMAT_CHARS) {
        throw new Error("MongoDB query is too large to format safely.");
    }

    const indentUnit = settings.useTabs ? "\t" : " ".repeat(settings.tabWidth ?? DEFAULT_SQL_FORMATTER_SETTINGS.tabWidth);
    const state: FormatState = { out: "", indentLevel: 0, atLineStart: true, pendingSpace: false, chainIndent: false, pendingChainCall: false, stack: [] };

    for (let index = 0; index < text.length; index++) {
        const char = text[index] ?? "";
        const next = text[index + 1] ?? "";

        if (char === '"' || char === "'" || char === "`") {
            const literal = readQuotedLiteral(text, index, char);
            appendToken(state, literal.value, indentUnit);
            index = literal.end;
            continue;
        }

        if (char === "/" && next === "/") {
            const comment = readLineComment(text, index);
            appendToken(state, comment.value, indentUnit);
            index = comment.end;
            continue;
        }

        if (char === "/" && next === "*") {
            const comment = readBlockComment(text, index);
            appendToken(state, comment.value, indentUnit);
            index = comment.end;
            continue;
        }

        if (char === "/" && looksLikeRegexLiteral(text, index)) {
            const regex = readRegexLiteral(text, index);
            appendToken(state, regex.value, indentUnit);
            index = regex.end;
            continue;
        }

        if (/\s/.test(char)) {
            state.pendingSpace = !state.atLineStart;
            continue;
        }

        if (char === "." && shouldBreakBeforeDot(text, index)) {
            newline(state, indentUnit);
            state.chainIndent = true;
            state.pendingChainCall = true;
            appendToken(state, ".", indentUnit);
            continue;
        }

        if (char === "{" || char === "[" || char === "(") {
            appendToken(state, char, indentUnit);
            const expanded = char !== "(" && shouldExpandOpening(text, index);
            const isChainCall = char === "(" && state.pendingChainCall;
            state.stack.push({ char, expanded, chainCall: isChainCall });
            if (isChainCall) state.indentLevel++;
            state.pendingChainCall = false;
            if (expanded) {
                state.indentLevel++;
                newline(state, indentUnit);
            }
            continue;
        }

        if (char === "}" || char === "]" || char === ")") {
            const frame = popMatchingFrame(state, char);
            if (frame?.expanded) {
                if (!state.atLineStart) newline(state, indentUnit, -1);
                else state.indentLevel = Math.max(0, state.indentLevel - 1);
            }
            if (frame?.chainCall) {
                state.indentLevel = Math.max(0, state.indentLevel - 1);
            }
            appendRaw(state, char, indentUnit);
            continue;
        }

        if (char === ",") {
            appendToken(state, ",", indentUnit);
            newline(state, indentUnit);
            continue;
        }

        if (char === ":") {
            trimTrailingSpaces(state);
            appendRaw(state, ": ", indentUnit);
            state.pendingSpace = false;
            continue;
        }

        appendToken(state, char, indentUnit);
    }

    return cleanupFormattedMongoText(state.out);
}

function appendToken(state: FormatState, token: string, indentUnit: string) {
    if (state.atLineStart) {
        state.out += indentUnit.repeat(Math.max(0, state.indentLevel + (state.chainIndent ? 1 : 0)));
        state.atLineStart = false;
    } else if (state.pendingSpace && shouldInsertPendingSpace(state.out, token)) {
        state.out += " ";
    }
    state.out += token;
    state.pendingSpace = false;
    state.chainIndent = false;
}

function appendRaw(state: FormatState, token: string, indentUnit: string) {
    if (state.atLineStart) {
        state.out += indentUnit.repeat(Math.max(0, state.indentLevel + (state.chainIndent ? 1 : 0)));
        state.atLineStart = false;
    }
    state.out += token;
    state.pendingSpace = false;
    state.chainIndent = false;
}

function newline(state: FormatState, indentUnit: string, indentDelta = 0) {
    trimTrailingSpaces(state);
    if (!state.out.endsWith("\n")) state.out += "\n";
    state.indentLevel = Math.max(0, state.indentLevel + indentDelta);
    state.atLineStart = true;
    state.pendingSpace = false;
    state.chainIndent = false;
    void indentUnit;
}

function shouldInsertPendingSpace(output: string, token: string): boolean {
    const previous = lastNonWhitespace(output);
    if (!previous) return false;
    if ([".", "(", "[", "{"].includes(previous)) return false;
    if ([".", ")", "]", "}", ",", ":"].includes(token)) return false;
    return true;
}

function shouldExpandOpening(text: string, index: number): boolean {
    const close = matchingClose(text[index] ?? "");
    const nextNonSpace = findNextNonWhitespace(text, index + 1);
    if (nextNonSpace == null || text[nextNonSpace] === close) return false;
    return true;
}

function popMatchingFrame(state: FormatState, close: string): { char: string; expanded: boolean; chainCall?: boolean } | undefined {
    const expectedOpen = close === "}" ? "{" : close === "]" ? "[" : "(";
    for (let index = state.stack.length - 1; index >= 0; index--) {
        const frame = state.stack[index];
        state.stack.splice(index, state.stack.length - index);
        if (frame?.char === expectedOpen) return frame;
    }
    return undefined;
}

function shouldBreakBeforeDot(text: string, index: number): boolean {
    const method = readIdentifier(text, findNextNonWhitespace(text, index + 1) ?? index + 1);
    if (!method || !CHAIN_METHODS.has(method)) return false;
    const previousNonSpace = findPreviousNonWhitespace(text, index - 1);
    if (previousNonSpace == null) return false;
    return text[previousNonSpace] === ")";
}

function readQuotedLiteral(text: string, start: number, quote: string): { value: string; end: number } {
    let index = start + 1;
    while (index < text.length) {
        const char = text[index] ?? "";
        if (char === "\\") {
            index += 2;
            continue;
        }
        if (char === quote) return { value: text.slice(start, index + 1), end: index };
        index++;
    }
    return { value: text.slice(start), end: text.length - 1 };
}

function readLineComment(text: string, start: number): { value: string; end: number } {
    const end = text.indexOf("\n", start);
    if (end < 0) return { value: text.slice(start), end: text.length - 1 };
    return { value: text.slice(start, end), end: end - 1 };
}

function readBlockComment(text: string, start: number): { value: string; end: number } {
    const end = text.indexOf("*/", start + 2);
    if (end < 0) return { value: text.slice(start), end: text.length - 1 };
    return { value: text.slice(start, end + 2), end: end + 1 };
}

function readRegexLiteral(text: string, start: number): { value: string; end: number } {
    let index = start + 1;
    let inCharClass = false;
    while (index < text.length) {
        const char = text[index] ?? "";
        if (char === "\\") {
            index += 2;
            continue;
        }
        if (char === "[") inCharClass = true;
        else if (char === "]") inCharClass = false;
        else if (char === "/" && !inCharClass) {
            let end = index;
            while (/[a-z]/i.test(text[end + 1] ?? "")) end++;
            return { value: text.slice(start, end + 1), end };
        }
        index++;
    }
    return { value: text.slice(start), end: text.length - 1 };
}

function looksLikeRegexLiteral(text: string, index: number): boolean {
    const previous = findPreviousNonWhitespace(text, index - 1);
    if (previous == null) return true;
    return "({[,=:!&|?".includes(text[previous] ?? "");
}

function readIdentifier(text: string, start: number): string {
    let index = start;
    while (index < text.length && /[A-Za-z0-9_$]/.test(text[index] ?? "")) index++;
    return text.slice(start, index);
}

function matchingClose(open: string): string {
    if (open === "{") return "}";
    if (open === "[") return "]";
    return ")";
}

function findNextNonWhitespace(text: string, start: number): number | null {
    for (let index = start; index < text.length; index++) {
        if (!/\s/.test(text[index] ?? "")) return index;
    }
    return null;
}

function findPreviousNonWhitespace(text: string, start: number): number | null {
    for (let index = start; index >= 0; index--) {
        if (!/\s/.test(text[index] ?? "")) return index;
    }
    return null;
}

function lastNonWhitespace(text: string): string | null {
    const index = findPreviousNonWhitespace(text, text.length - 1);
    return index == null ? null : (text[index] ?? null);
}

function trimTrailingSpaces(state: FormatState) {
    state.out = state.out.replace(/[ \t]+$/g, "");
}

function cleanupFormattedMongoText(text: string): string {
    return text
        .split("\n")
        .map((line) => line.replace(/[ \t]+$/g, ""))
        .join("\n")
        .replace(/\n{3,}/g, "\n\n")
        .trim();
}